Keiichi Mimura

Movement discrimination by the visual system of flies

Summary1.A glass microelectrode was inserted into the optic lobes of fleshflies (Boettcherisca peregrina) and discharges responding to the movement of a spot of light were recorded.2.Units responding to moving spot were classified into four types: non-directional, one directional, semi-integrative and integrative types. In addition, there was an “alerting” unit which discharged phasically to movement of a spot in any direction and adapted quickly, and an “inhibitory” unit in which discharges were inhibited by movement of a spot in any direction although a preferred direction was seen slightly.3.Units of the non-directional type with relatively narrow receptive fields were found in the medulla only, while those with wide fields were in the lobula and the pathway to the central brain.4.Units of the one directional type, which discharge to a preferred direction, were found in the region of the medulla to the lobula regardless of the size of the receptive field.5.Units of the semi-integrative type, which possess a receptive field apparently formed by the combination of two or more fields of the one directional type and sometimes discharge dominantly to vertical movement at the front along the head axis, were found in all regions of the medulla to such central parts as the optic peduncle.6.Units of the integrative type, which respond to such complex, but continuous movement as a circular motion of objects, were found in the central region from the lobula to the pathways to the brain.7.Four types of relationships were found between the speed of the moving spot and the discharge rate: a, the discharge rate increased proportionally to the logarithm of the increase of the speed; b, the discharge rate was not altered by the speed changes; c, the discharge rate became maximal at a particular speed; d, the discharge rate was decreased or inhibited with increase of the speed.Type a was mainly seen in units of the one directional type with a wide receptive field and in units of the semi-integrative type, and was distributed over the region from the medulla to the lobula. Type b was found in units of the non-directional type with a narrow receptive field, and was situated in the medulla only. Type c was related with units of the directional and integrative types, and located in the central region of the optic lobes. Type d, seen in only few number, was found in the pathway to the central brain.8.Orderly arrangement of the units, which suggests a neural mechanism for directional selectivity, was electrophysiologically observed.9.It is concluded that the analytical processing of the direction and speed of movement is conducted in the region of the medulla to the lobula, and that the neural integration is performed in the central part of the optic lobes, the lobula and the pathway to the central brain.

Neural mechanisms, subserving directional selectivity of movement in the optic lobe of the fly

Summary1.A glass microelectrode was inserted into the unit responding to movements of a spot in the lobula or, on rare occasions, in the medulla of the optic lobe of fleshflies (Boettcherisca peregrina).2.By the sequential presentation of several or two stationary spots placed along the preferred-null axis of the directionally selective unit and by the turning on and off of a stationary spot (test stimulus) placed along the preferred-null axis at various distances from another continuously lighted, fixed spot (conditioned stimulus), it is demonstrated that spatial, excitatory effects were produced on the preferred direction side of the conditioned spot, and simultaneously, spatial, inhibitory effects were seen on the side of the null direction. Therefore, it is considered that movement perception is analyzed on the basis of the stationary and elemental light sensation and is completed by both the mechanism of excitation in the preferred direction and inhibition in the null direction.3.The field with excitatory effect is relatively wider (20 ° or more in visual angle) than that with inhibitory one (8 °–20 °, rarely more than 20 °). The inhibitory effect decreases gradually with increasing distance from the conditioned spot stimulus, while the excitatory effect increases with each 5 ° of separation in visual angle from the conditioned spot. Therefore, it is assumed that the neural mechanism for excitatory effects is different from that for inhibitory effects.4.Movements of a bright slit on a dark background and a dark slit on a light background were given using various slit lengths. The discharge rate in the directionally selective unit shows an increase, a decrease or an increase after a decrease by increasing the length of the slit. These three kinds of responses are explained by the width of the interactivity between the excitatory and inhibitory fields to spot stimulation.5.The neural organization of excitatory and inhibitory field effects underlying the directional selectivity in movement perception is discussed from the morphological view point.

Development of Visual Pattern Discrimination in the Fly Depends on Light Experience

Pattern discrimination by dewinged walking flies (Boettcherisca peregrina) was tested in behavioral experiments. After emergence, the flies were deprived of light or visual patterns. Deprivation impaired the normal development of visual pattern discrimination without impairing phototaxis. Flies kept in a lighted, white, unpatterned environment could not discriminate visual patterns, nor could flies kept in continuous darkness. These results indicate that there is considerable plasticity in the structure of the visual system of these flies.

Analysis of visual information in lamina neurones of the fly

Summary1.Spike discharges accompanying slow electrical deflections were extracellularly recorded from the plexus between the lamina and medulla of the optic lobe of the fleshflyBoettcherisca peregrina by means of glass microcapillaries. The eye was stimulated with a spot-like light source, and sometimes a slit of light was used.2.Elicitation of the spikes was found to be related with the slow electrical deflections.3.The spike response patterns were used to study the organization of the receptive field, colour sensitivity and movement.4.From the response to instantaneous flash of a spot of light placed at varying distances from a continuously illuminated conditioned spot of light within the receptive field, the interactions of responses within the receptive field were elucidated, and in particular the lateral inhibitory and excitatory processes were clearly demonstrated. It was assumed that the latter processes were due to the disinhibition of the lateral inhibitory processes.5.The contributions of the activities of the lamina neurones demonstrated here to movement detection are discussed.

A simplified method for crosscorrelation analysis

Abstract A simple method of obtaining a crosscorrelogram between two waveforms has been described. Comparison between the formal method of crosscorelation and the simplified procedure demonstrates a good similarity of the results obtained.

The effect of partial covering of the eye on the results of selective deprivation of visual pattern in the fly

Visual deprivation experiments have demonstrated that the development of pattern discrimination in the fly depends on experience in the early period after emergence. Based on this finding, a behavioral study was done in which flies had their eyes partially covered during selective deprivation treatment. This study demonstrated that several simple visual patterns are mainly identified in a restricted, pattern-specific region of the compound eyes, and also that the effect of visual deprivation is produced in the unilateral compound eye and is not transferred to the contralateral side.

A simplified method for autocorrelation analysis in electroencephalography.

Abstract a simple method of obtaining an auto-correlogram of the wave form has been described. Comparison between the orthodox method of auto-correlation and the simplified procedure demonstrates a good similarity of the results, provided that the wave form under analysis is of adequate lenght.

Discrimination of some visual patterns inDrosophila melanogaster

SummaryStudies of phototactic behaviour of the flesh fly have demonstrated that some illuminated visual patterns can be discriminated (Mimura 1981 b). It was further suggested that the receptive field patterns of the photoreceptors contribute to pattern discrimination (Mimura 1981a). On the basis of the phototactic choice behaviour in some of the photoreceptor mutants ofDrosophila melanogaster, this study was conducted to identify which photoreceptors among R1 to R8 subserve the pattern discrimination. 1.Wild typeDrosophila showed almost the same pattern discrimination as seen in the flesh fly. Rankings of the tested patterns were as follow: first, pattern A; second, pattern C; third, patterns B, D and E; fourth, patterns F, G and H (cf. Fig. 2).2.Pattern discrimination in the mutantsev was almost the same as in wild type, except that pattern F was less ‘attractive’ than patterns G and H.3.Neither mutantsora norsev;ora could discriminate the tested patterns at all.4.The number of visits to pattern targets in wild type was larger than insev. The reaction to the midpoint between two arranged targets was less in wild type than insev.5.Phototaxis to illuminated non-pattern target was demonstrated even in the mutantsora andsev;ora. Regardless of pattern or non-pattern targets, the number of visits to targets increased with increasing target brightness in wild type, while in all the tested mutants it was reduced at the highest brightness of the target (Fig. 4).From the above findings it was concluded that R1-6 photoreceptors mainly subserve the pattern discrimination, R7 plays a subsidiary role, and R8 does not contribute.

Electrophysiological evidence for interaction between retinula cells in the flesh-fly

SummaryIn the electrical response of retinula cells to polarized light in the flesh-flyBoettcherisca peregrina, the polarization plane which showed the maximum sensitivity (Polmax phase) to illumination by a small spot of light just large enough to cover only one retinula cell was found to differ from that with illumination by a larger spot of light which included adjacent cells. There was a difference of about 30°.This difference in Polmax phase was assumed to indicate the occurrence of interaction between retinula cells even in the fly photoreceptor having rhabdom of the open type. This assumption was confirmed by the following experiments. (1) Under selective adaptation by a large spot of polarized light so as to eliminate the interaction effect, the Polmax phase was found to be the same as that measured by a small spot even though the measurement had been made using a large spot of light. (2) The responses to polarized light illuminated from along some restricted off-axes showed a 60° shift in the Polmax phase in comparison to those obtained from along the other axes. (3) The spectral sensitivity curves to illumination from along off-axes were almost all the same and were for the peripheral retinula cells. (4) The receptor potentials were found to increase in amplitude in a certain limited off-axis area that corresponded to the specific off-axis direction of illumination which had resulted in a shift of the Polmax phase.It is concluded from these results that the peripheral retinula cells in the flesh-fly demonstrate interaction between certain two adjacent retinula cells. This interaction is positive but not a simple algebraic sum of the activity of two cells.

A simplified method for determining the average response time-pattern of the evoked potential in electroencephalography

Abstract A method has been described to obtain the average response time-pattern of evoked potentials in the electroencephalogram. This method is particularly useful for short recording periods. Comparison has been made to Dawsons summation technique of demonstrating evoked responses; improvement and clarity of the calculated responses is shown.